From the prior art, it is known to implement the oil supply of transmissions in the passenger car and commercial vehicle sectors via positive displacement pumps which are fixed displacement pumps acting as main pumps and which are driven by the internal combustion engine of the motor vehicle. It is further known from the prior art to provide an electric auxiliary pump in the case of a transmission of a hybrid drive train of a motor vehicle in order to ensure the oil supply when the internal combustion engine is stopped, for example, when the vehicle is at a standstill or during purely electric driving. The gear select interlock during electric driving as well as the cooling of the transmission are to be ensured by the auxiliary pump. This auxiliary pump is generally operated only when the main oil pump, which is driven by the internal combustion engine or by yet another prime mover, can no longer ensure the required flow rate or oil pressure.
On the basis of measurements, it was determined that, in vehicles comprising a main pump, which is driven by the internal combustion engine of the vehicle, and comprising an electric auxiliary pump, the direction of rotation of the internal combustion engine, and therefore the rotation of the crankshaft, can reverse during an internal combustion engine stopping process, whereby the internal combustion engine can counter-oscillate/kick back in the opposite direction of rotation for a short time. This disadvantageously results in an oil leakage in the main pump which is driven by the internal combustion engine and which is generally a sliding vane pump. The oil leakage is caused by the fact that a sliding vane pump functions correctly in only one direction of rotation and, upon rotation in the opposite direction, a gap forms between the vane and the wall, which causes a leakage.
This oil leakage of the main pump results in non-defined rotational speeds of the electric auxiliary pump and, therefore, undefined pressure and lubricating oil conditions, which negatively influence the durability of the transmission.